In recent years, a three-dimensional semiconductor memory such as a three-dimensional NAND flash memory has been developed in order to increase the storage capacity of a semiconductor memory. A three-dimensional NAND flash memory is normally produced by performing a plasma etching process on a multi-layer film in which insulating films that differ in dielectric constant are alternately stacked to form a hole or a trench. Examples of the multi-layer film include a multi-layer film in which a silicon oxide film and a silicon nitride film are stacked.
Since the multi-layer film is normally subjected to plasma etching while processing two or more films (e.g., silicon oxide film and silicon nitride film) that differ in properties without changing the etching conditions, it is necessary to employ etching conditions that are appropriate for all of the films included in the multi-layer film.
Since the multi-layer film normally has a thickness greater than that of a single-layer film, the etching time tends to increase when subjecting the multi-layer film to plasma etching as compared with the case of subjecting a single-layer film to plasma etching. Therefore, a hole or the like may be clogged by a deposited film, an abnormality in shape (e.g., bowing) may occur, or the mask may disappear when subjecting the multi-layer film to plasma etching.
As a method for solving the problems that may occur when subjecting the multi-layer film to plasma etching, Patent Literature 1 discloses a method that etches a multi-layer film that includes a silicon oxide film and a silicon nitride film using a process gas that includes a linear saturated fluorohydrocarbon compound represented by CxHyFz (wherein x is 4, y is an integer equal to or larger than 4, and z is a positive integer, provided that y+z is 10).
Patent Literature 1 states that the method disclosed in Patent Literature 1 can selectively etch the multi-layer film with respect to the mask, and form a hole or the like having a good shape while preventing a situation in which a hole or the like is clogged by a deposited film.
However, a further improvement in etching rate has been desired from the viewpoint of productivity.
Patent Literature 2 discloses a method that etches a silicon-containing film using a process gas that includes a fluorohydrocarbon compound that is represented by C4H2F6, C4H3F5, or C4H4F4, and includes an alicyclic structure or an unsaturated bond.
Patent Literature 2 discloses CF4, C4F6, and the like as a second gas that may be used in combination with the fluorohydrocarbon compound.
However, when a plasma etching process is performed using the process gas disclosed in Patent Literature 2 that includes the fluorohydrocarbon compound that includes an alicyclic structure or an unsaturated bond, a hole or the like is easily clogged. Therefore, the method disclosed in Patent Literature 2 is not suitable for fine processing.